The present invention is drawn to methods and compositions for obscuring immune recognition in a mammal. More particularly, the present invention is drawn to methods of encapsulating tissue within a hydrogel matrix.
The body defends itself from infectious agents through an immune response. Broadly speaking, the body has many layers of defense, including physical barriers like the skin, protective chemical substances, the blood and tissue fluids, and the physiologic reactions of tissues to injury or infection. The most effective defense strategy, however, is carried out by cells that have evolved specialized abilities to recognize and eliminate potentially injurious substances.
The response of a body to an infection occurs in the form of inflammation. An inflammatory response involves the passage of fluids, proteins, and cells from the blood into focal areas and tissues. The result is the local delivery of agents that can effectively combat infections. The process involves inflammatory cells, products of inflammatory cells, blood proteins, and pathways of response. Initiation of an inflammatory response begins by an increase in blood flow to infected tissues and by the separation of cells lining the blood vessels or capillaries, followed by emigration of cells into the involved tissue.
The immune response involves both humoral and cellular immune responses. Both responses are essential components of the defense against pathogenic bacteria, viruses, parasites, and other foreign objects. Cellular immunity is mediated by a class of white blood cells called lymphocytes. These cells originate from stem cells in the bone marrow and migrate to the thymus gland. While in the thymus, they undergo differentiation before emigrating to the peripheral lymphoid organs. Cells processed in the thymus are referred to as T-lymphocytes or T-cells. T-cells can destroy cells infected by various types of viruses or intracellular bacteria. Humoral immunity, or the humoral response, is mediated by antibodies. Antibodies are protein molecule synthesized by another class of lymphocyte called B-cells. B-cells also originate from stem cells in the bone marrow, but do not enter the thymus. B-cells are found in all peripheral lymphoid organs, and the antibodies they secrete are found throughout the body. The immune response is a complex intricately regulated sequence of events involving these cell types. It is triggered when an antigen, or foreign object, enters the body.
Among the major obstacles in research directed to pancreatic islet transplantation for the treatment of diabetes is an inability to induce permissive acceptance of xenograft tissue transplants in the host mammal. Current methods of transplantation must suppress immune response by the host mammal that may lead to rejection of the transplanted cells and loss of islet function. Many transplantation approaches require the host to take general immunosuppressive agents to prevent a host immune response from destroying the transplanted tissue. However, such immunosuppressive agents are undesirable because they reduce the immune response of the host generally, and thus can lead to poor health. Thus, there is also a need in the art for a simple, non-invasive method of introducing a transplant into a host without requiring general immunosuppressive agents.
The present invention provides a method of obscuring immune recognition of a transplant by encapsulating the tissue of the transplant within a hydrogel matrix comprising highly polar amino acids and gelatin fragments, such as denatured collagen fragments, having exposed polar groups. The exposed polar groups of the collagen fragments and the polar amino acids enable the matrix to bind to cell surface proteins, thereby obscuring the cell surface proteins, particularly from specific high affinity antibodies of the host organism. Since the high affinity antibodies are unable to recognize the protein structure of the foreign tissue, the antibodies are unable to stimulate immune response and destroy the transplant. The methods and compositions of the present invention are even effective in obscuring immune recognition of xenograft transplants, such that permissive acceptance of the xenograft transplant by the host organism is achieved.
In particular, the present invention provides a method of obscuring immune recognition of a transplant by a host mammal. The method includes providing tissue for suitable use in the transplant, wherein the tissue comprises cells having cell surface proteins. The tissue is encapsulated in the hydrogel matrix to form a transplant, wherein the matrix binds to the cell surface proteins of the encapsulated tissue. Thereafter, the thus-formed transplant may be implanted into a transplant site in a mammal. For example, the transplant may be implanted intramuscularly, subcutaneously, intra-organ, intravascularly, or in the peritoneal cavity.
In some embodiments, the transplant site may be prepared prior to implanting the above-described transplant by applying a buffer medium to the transplant site, wherein the buffer medium comprises at least one nitric oxide inhibitor, such as L-cysteine and aminoguanidine. For example, the applying step may comprise injecting about 10 to about 300 cc of the buffer medium into the transplant site prior to implantation. Periodically, after implantation of the transplant, further applications of the buffer medium to the transplant site may be made.